How to delete all my music off my iPhone 5s?

Everything has been updated, but even so, my iPhone won't sync properly. When I go on my Mac and look at my iTunes, my library is exactly how I want it to be. So I try and sync my iPhone and all the songs are greyed out in my iTunes under devices. I go on my phone, and I still have all my music, it's just not how I want it because I've recently gone through my library and unchecked a bunch of old songs etc. So I would like my iPhone to be up to date.

I figured the easiest fix would be to delete all the music off my iPhone and then try and sync it again. IIm hoping that will do the trick. So how do I delete all the music off my iPhone… Or does anyone have any other ideas?

Settings > General > Usage > Manage Storage > Music > Edit > All Songs (red button)